| // Copyright 2014 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| namespace ui { |
| |
| class AXTree; |
| |
| // A class to create all possible trees with <n> nodes and the ids [1...n]. |
| // |
| // There are two parts to the algorithm: |
| // |
| // The tree structure is formed as follows: without loss of generality, |
| // the first node becomes the root and the second node becomes its |
| // child. Thereafter, choose every possible parent for every other node. |
| // |
| // So for node i in (3...n), there are (i - 1) possible choices for its |
| // parent, for a total of (n-1)! (n minus 1 factorial) possible trees. |
| // |
| // The second part is the assignment of ids to the nodes in the tree. |
| // There are exactly n! (n factorial) permutations of the sequence 1...n, |
| // and each of these is assigned to every node in every possible tree. |
| // |
| // The total number of trees returned for a given <n>, then, is |
| // n! * (n-1)! |
| // |
| // n = 2: 2 trees |
| // n = 3: 12 trees |
| // n = 4: 144 trees |
| // n = 5: 2880 trees |
| // |
| // This grows really fast! Luckily it's very unlikely that there'd be |
| // bugs that affect trees with >4 nodes that wouldn't affect a smaller tree |
| // too. |
| class TreeGenerator { |
| public: |
| TreeGenerator(int node_count); |
| |
| int UniqueTreeCount() const; |
| |
| void BuildUniqueTree(int tree_index, AXTree* out_tree) const; |
| |
| private: |
| int node_count_; |
| int unique_tree_count_; |
| }; |
| |
| } // namespace ui |
